3D crumbled MXene for high-performance supercapacitors

MXene materials have recently attracted considerable attention in energy storage application owing to their metallic conductivity, 2D structure and tunable surface terminations. However, the restacking of 2D MXene nanosheets hinders the ion transport and accessibility to the surface, resulting in adverse effect on their electrochemical performances. Here, with the assistance of hexamethylenetetramine (C₆H₁₂N₄), 2D Ti₃C₂T_x MXene nanosheets were fabricated into a 3D architecture with crumbled and porous structure through an electrostatic self-assembly followed by annealing. The resultant 3D structure can expose massive active sites and facilitates the ion transport, which is beneficial for sufficient utilization of the outstanding superiorities of the MXene. Therefore, as a pseudocapacitive material, the 3D crumpled and porous Ti₃C₂T_x MXene shows a gravimetric capacitance of 333 F/g at 1 A/g, and maintains 261 F/g and 132 F/g at ultrahigh current densities of 100 A/g and 1000 A/g, respectively, revealing promising potential for application in supercapacitors.     

Porous and free-standing Ti_3C_2T_x-RGO film with ultrahigh gravimetric capacitance for supercapacitors

MXene-based electrode materials exhibit favorable supercapacitor performance in sulfuric acid due to praised pseudocapacitance charge storage mechanism.However,self-stacking of conventional MXene electrodes severely restricts their electrochemical performance,especially at high loading.Herein,a flexible cross-linked porous Ti₃C₂T_x-MXene-reduced graphene oxide(Ti₃C₂T_x-RGO) film is skillfully designed and synthesized by microscopic ...     

Intertwined Titanium Carbide MXene within a 3 D Tangled Polypyrrole Nanowires Matrix for Enhanced Supercapacitor Performances

The exploration of the rational design and synthesis of unique and robust architectured electrodes for the high capacitance, rate capability, and stability of supercapacitors is crucial to the future of energy storage technology. Herein, an in situ synthesis of multilayered titanium carbide MXene tightly caging within a 3 D conducting tangled polypyrrole (PPy) nanowire (NW) network is proposed as an effective strategy to prevent the aggregation of MXene, profoundly enhancing the electrochemical performance of the supercapacitor. Owing to the beneficial effects of an ideal 3 D interconnected porous structure and high electrical conductivity, the obtained electrode exhibits fast charge and ion transport kinetics as well as full usage of active material. As expected, the 3 D Ti₃C₂T_x@PPY NW exhibits a specific capacitance five times higher than that of pristine MXene (610 F g⁻¹), a good rate capability up to a current density of 25 A g⁻¹, and excellent stability with 100 % retention after 14 000 cycles at 4 A g⁻¹, outperforming the known state-of-the-art MXene-based supercapacitor. Our work provides a facile method for enhancing the performance of MXene-based energy storage devices.     

Layer-by-layer engineered Co-Al hydroxide nanosheets/graphene multilayer films as flexible electrode for supercapacitor

Multilayer films of Co-Al layered double hydroxide nanosheets (Co-Al LDH-NS) and graphene oxide (GO) were fabricated through layer-by-layer (LBL) assembly. By using a three-electrode system, the electrochemical performances of the films were investigated to evaluate their potential as electrode materials to be used in flexible supercapacitor devices. The Co-Al LDH-NS/GO multilayer films exhibited a high specific capacitance of 880 F/g and area capacitance of 70 F/m(2) under the scan rate of 5 mV/s. And the film exhibited good cycle stability over 2000 cycles. After treating the films at 200 °C in H(2) atmosphere, the specific capacitance and area capacitance were largely increased up to 1204 F/g and 90 F/m(2) due to partial reduction of GO. A flexible electrode by depositing Co-Al LDH-NS/GO multilayer film onto PET substrate was prepared to show the potential of Co-Al LDH-NS/GO films for flexible energy storage.     

Nitrogen-Doped Porous MXene (Ti3C2) for Flexible Supercapacitors with Enhanced Storage Performance

Flexible supercapacitors (FSCs) are limited in flexible electronics applications due to their low energy density. Therefore, developing electrode materials with high energy density, high electrochemical activity, and remarkable flexibility is challenging. Herein, we designed nitrogen-doped porous MXene (N-MXene), using melamine-formaldehyde (MF) microspheres as a template and nitrogen source. We combined it with an electrospinning process to produce a highly flexible nitrogen-doped porous MXene nanofiber (N-MXene-F) as a self-supporting electrode material and assembled it into a symmetrical supercapacitor (SSC). On the one hand, the interconnected mesh structure allows the electrolyte to penetrate the porous network to fully infiltrate the material surface, shortening the ion transport channels; on the other hand, the uniform nitrogen doping enhances the pseudocapacitive performance. As a result, the as-assembled SSC exhibited excellent electrochemical performance and excellent long-term durability, achieving an energy density of 12.78 Wh kg⁻¹ at a power density of 1080 W kg⁻¹, with long-term cycling stability up to 5000 cycles. This work demonstrates the impact of structural design and atomic doping on the electrochemical performance of MXene and opens up an exciting possibility for the fabrication of highly FSCs.     

超级电容器用石墨烯薄膜：制备、基元结构及表面调控

石墨烯薄膜是一种以石墨烯纳米片为基元结构的宏观体,通过合理的结构设计和表面修饰使其具有优异的电学、力学和热学性能,将在电化学储能、电子器件、健康和环保等领域具有潜在的应用。本文主要综述了从石墨烯基元调控到二维宏观膜组装以及石墨烯薄膜在超级电容器应用中的研究进展。主要介绍了石墨烯薄膜的简易制备方法,并详细介绍了通过对石墨烯基元的结构调控和表面修饰来优化石墨烯薄膜电化学性能的两大策略,最后对石墨烯薄膜应用所面临的挑战和未来的发展进行了总结与展望。     

All-solid-state flexible microsupercapacitor based on two-dimensional titanium carbide

MXenes,serving as a novel family of two-dimensional(2D) metal carbides,have attracted great research interest as one of the promising electrode materials due to the unique properties.However,to our best knowledge,the 2D titanium carbide(one kind of MXene) used in constructing microsupercapacitors(MSCs) has not yet been reported to date.To this end,we firstly produce the MXene films on various kinds of substrates including polyethylene terephthalate(PET),silicon oxide film and titanium plate through vacuum-filtrating and subsequent controlled transferring.On this basis,flexible all-solid-state symmetric MSCs on PET substrate based on MXene films are fabricated by micro-fabrication process using polyvinyl alcohol(PVA)/H_2SO_4 as gel electrolyte.The results show that the as-made MSC has an ultrahigh rate performance with the scan rate of up to 1000Vs~(-1) as well as an ultrafast frequency response(τ_0 = 0.5 ms).In addition,the MSC delivers a large volumetric capacitance of 1.44 F cm~(-3),a high volumetric energy density(0.2 mWh cm~(-3) at the current density of 0.288 A cm~(-3) and a good cycling stability.Our research results presented here may pave the way for a new potential application of MXene in micro-power suppliers and micro-energy storage devices.     

Effect of carboxylic acid groups on the supercapacitive performance of functional carbon frameworks derived from bacterial cellulose

Three-dimensional(3D) carbonaceous materials derived from bacterial cellulose(BC) has been introduced as electrode for supercapacitors in recent. Here, we report a simple strategy for the synthesis of functional carbon frameworks through 2,2,6,6-tetramethylpilperidine 1-oxyl radical(TEMPO)-mediated oxidation of bacterial cellulose(BC) followed by carbonization. TEMPO-mediated oxidation can efficiently convert the hydroxyls on the surface of BC to carboxylate groups to improve electrochemical activity. Because of its high porosity, good hydrophilicity, rich oxygen groups, and continuous ion transport in-between sheet-like porous network, the TEMPO-oxidized BC delivers a much higher gravimetric capacitance(137.3 F/g) at low annealing temperature of 500℃ than that of pyrolysis BC(31 F/g) at the same annealing temperature. The pyrolysis modified BC obtained at 900℃ shows specific capacitance(160.2 F/g), large current stability and long-term stability(84.2% of its initial capacitance retention after 10,000 cycles).     

Electrodeposited NiSe_2 on carbon fiber cloth as a flexible electrode for high-performance supercapacitors

A flexible electrode of nickel diselenide/carbon fiber cloth(NiSe_2/CFC) is fabricated at room temperature by a simple and efficient electrodeposition method. Owing to NiSe_2 character of nanostructure and high conductivity, the as-synthesized electrodes possess perfect pseudocapacitive property with high specific capacitance and excellent rate capability. In three-electrode system, the electrode specific capacitance of the NiSe_2/CFC electrode varies from 1058 F g~(-1) to 996.3 F g~(-1) at 2 A g~(-1) to 10 A g~(-1) respectively, which shows great rate capability. Moreover, the NiSe_2 electrode is assembled with an active carbon(AC) electrode to form an asymmetric supercapacitor with an extended potential window of 1.6 V. The asymmetric supercapacitor possesses an excellent energy density 32.7 Wh kg~(-1) with a power density 800 W kg~(-1) at the current density of 1 A g~(-1). The nanosheet array on carbon fiber cloth with high flexibility, specific capacitance and rate capacitance render the NiSe_2 to be regarded as the promising material for the high performance superconductor.     

基于三维多孔石墨烯/含钛共轭聚合物复合多孔薄膜的柔性全固态超级电容器

采用Fe~(3+)离子交联的方法制备氧化石墨烯水凝胶,经化学还原制备出一种新型的三维多孔石墨烯薄膜材料命名为rGO-Fe;通过电化学聚合法在rGO-Fe基底上进一步制备了一种三维多孔石墨烯/含钛共轭聚合物复合薄膜材料,命名为r GO-Fe/P(EDOT:P3C)-1-Ti。作为一种新型复合薄膜材料,rGO-Fe/P(EDOT:P3C)-1-Ti较rGO-Fe具有更好的抗拉伸性能,平均厚度为3μm的rGO-Fe/P(EDOT:P3C)-1-Ti薄膜,可承受载荷拉力0.97 N,优于相同厚度的rGO-Fe薄膜(0.76 N)。将rGO-Fe/P(EDOT:P3C)-1-Ti薄膜作为自支撑电极制备了柔性全固态超级电容器,表现出优良的电容性能,且在弯折状态下仍能正常工作。当电流密度为0.1 A?g~(-1)时,该柔性全固态超级电容器的质量比容量为71.13?F?g~(-1),面积比容量为101 mF?cm~(-2),当电流密度为0.6 A?g~(-1)时,其质量比容量为18.14 F?g~(-1),面积比容量为25.8 mF?cm~(-2)。     

多次聚合法制备多孔聚吡咯厚膜及其电化学容量性能

为了得到高面积比容量的聚吡咯(PPy)膜超级电容器电极材料, 用多次聚合法合成了PPy厚膜, 聚合电量分别为8、10和12 mAh·cm-2, 掺杂离子分别为氯离子和对甲基苯磺酸根离子(TOS-). PPy膜的电化学性能采用恒电流充放电、循环伏安(CV)和电化学阻抗谱(EIS)等方法测试. 研究表明, 多次聚合法可以制备表面平整且内部均匀多孔的PPy厚膜. 在聚合电量为12 mAh·cm-2时, 用Cl-、TOS-两种离子掺杂的PPy厚膜的面积比容量高达5 F·cm-2, 并表现出理想的电化学容量性能. 同时PPy-Cl厚膜的质量比容量达到330 F·g-1, PPy-TOS厚膜的质量比容量略低(191 F·g-1), 但具有更快的充放电速率. 与一次聚合法合成的PPy 薄膜相比, 多次聚合法合成的PPy厚膜的质量比容量没有降低. 通过场发射扫描电镜(SEM)观察了一次聚合法和多次聚合法制备的PPy厚膜的截面形貌, 并讨论了多次聚合法的合成机理.     

Capacitance and field-driven electron transport in electrochemically self-assembled nanoporous ZnO/dye hybrid films

Electrodeposited nanoporous ZnO/eosin Y hybrid films have been investigated in view of their potential applications in dye-sensitized solar cells and supercapacitors. Intensity-modulated photocurrent spectra were measured at different electrode potentials at films of different thicknesses. It was found that the results represent either the RC constant of the cell and surface recombination of photogenerated holes with electrons or the diffusion of photogenerated electrons and are dependent on the electron concentration in the ZnO, which is influenced by the film thickness, the electrode potential, and the light intensity. The results suggest that the porosity of the electrodeposited ZnO increases with the film thickness and the films therefore consist of two parts, a less porous part deposited in the first few minutes that exhibits field-driven electron transport and a more porous outer part where electron transport is by diffusion. The results are supported by frequency-dependent capacitance measurements, which also show that the material is suitable for supercapacitors.     

Three‐Dimensional Nitrogen‐Doped Hierarchical Porous Carbon as an Electrode for High‐Performance Supercapacitors

A facile and sustainable procedure for the synthesis of nitrogen‐doped hierarchical porous carbons with a three‐dimensional interconnected framework (NHPC‐3D) was developed. The strategy, based on a colloidal crystal‐templating method, utilizes nitrogenous dopamine as the precursor due to its unique properties, including self‐polymerization under mild alkaline conditions, coating onto various surfaces, a high carbonization yield, and well‐preserved nitrogen doping after heat treatment. The obtained NHPC‐3D possesses a high surface area of 1056 m² g^?1, a large pore volume of 2.56 cm³ g^?1, and a high nitrogen content of 8.2 wt %. The NHPC‐3D is implemented as the electrode material of a supercapacitor and exhibits a specific capacitance as high as 252 F g^?1 at a current density of 2 A g^?1. The device also shows a high capacitance retention of 75.7 % at a higher current density of 20 A g^?1 in aqueous electrolyte due to a sufficient surface area for charge accommodation, reversible pseudocapacitance, and minimized ion‐transport resistance, as a result of the advantageous interconnected hierarchical porous texture. These results showcase NHPC‐3D as a promising candidate for electrode materials in supercapacitors.     

Characterization of porous cobalt hexacyanoferrate and activated carbon electrodes under dynamic polarization conditions in a sodium-ion pseudocapacitor

We report here the activated carbon and cobalt hexacyanoferrate composite,which is applied as the electrode materials in symmetric supercapacitors containing a 1.0 M Na₂SO₄ aqueous electrolyte.This novel material combines high specific surface area and electrochemical stability of activated carbon with the redox properties of cobalt hexacyanoferrate,resulting in maximum specific capacitance of 329 F g^-1 with large voltage working window of 2.0 V.Electrochemical studies indicated that cobalt hexacyanoferrate introduces important pseudocapacitive properties accounting for the overall charge-storage process,especially when I<0.5 A g^-1.At lower gravimetric currents(e.g.,0.05 A g^-1)and up to 1.0 V,the presence of cobalt hexacyanoferrate improves the specific energy for more than 300%.In addition,to better understanding the energy storage process we also provided a careful investigation of the electrode materials under dynamic polarization conditions using the in situ Raman spectroscopy and synchrotron light Xray diffraction techniques.Interesting complementary findings were obtained in these studies.We believe that this novel electrode material is promising for applications regarding the energy-storage process in pseudocapacitors with long lifespan properties.     

皱褶表面介孔镍钴硫化物微球的制备及其超电性能

通过一步水热法分别合成了α-NiS、Co₃S₄和CoNi₂S₄纳米介孔电极材料,并研究了其电化学性能。 X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)研究表明,介孔硫化物是由单相纳米颗粒堆叠组装而成,其中二元系的CoNi₂S₄由纳米片自组装形成了具有皱褶表面的微球形貌。 电化学性能研究表明,二元系的CoNi₂S₄比α-NiS、Co₃S₄具有更高的比电容、更佳的倍率特性和优异的循环稳定性。 在扫描速率为5 mV/s时,CoNi₂S₄材料在6 mol/L KOH电解液中比电容高达1678.3 F/g,优于α-NiS (787.4 F/g)和Co₃S₄(1532.7 F/g),在扫描速率从5 mV/s增加到100 mV/s时,其电容保持率为45.8%,比α-NiS(30.2%)和Co₃S₄(29.3%)高出约15%。 在15A/g的电流密度下,经过900次循环充-放电后,二元系的CoNi₂S₄的电容仍保持在96.3%,库伦效率保持在94.3%左右,说明镍钴双金属硫化物具有优异的循环稳定性能和充放电可逆性。     

Designing N-doped graphene/ReSe_2/Ti_3C_2 MXene heterostructure frameworks as promising anodes for high-rate potassium-ion batteries

Developing high-performance anodes for potassium ion batteries(KIBs) is of paramount significance but remains challenging.In the normal sense,electrode materials are prepared by ubiquitous wet chemical routes,which otherwise might not be versatile enough to create desired heterostructures and/or form clean interfacial areas for fast transport of K-ions and electrons.Along this line,rate capability/cycling stability of resulting KIBs are greatly handicapped.Herein we present an all-chemical vapor deposition approach to harness the direct synthesis of nitrogen-doped graphene(NG)/rhenium diselenide(ReSe_2)hybrids over three-dimensional MXene supports as superior heterostructure anode material for KIBs.In such an innovative design,1 T'-ReSe2 nanoparticles are sandwiched in between the NG coatings and MXene frameworks via strong interfacial interactions,thereby affording facile K~+ diffusion,enhancing overall conductivity,boosting high-power performance and reinforcing structural stability of electrodes.Thus-constructed anode delivers an excellent rate performance of 138 mAh g^-1 at 10.0 A g^-1 and a high reversible capacity of 90 mAh g^-1 at 5 A g^-1 after 300 cycles.Furthermore,the potassium storage mechanism has been systematically probed by advanced in situlex situ characterization techniques in combination with first principles computations.     

A Microwave Synthesis of Mesoporous NiCo2O4 Nanosheets as Electrode Materials for Lithium‐Ion Batteries and Supercapacitors

A facile microwave method was employed to synthesize NiCo₂O₄ nanosheets as electrode materials for lithium‐ion batteries and supercapacitors. The structure and morphology of the materials were characterized by X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller methods. Owing to the porous nanosheet structure, the NiCo₂O₄ electrodes exhibited a high reversible capacity of 891 mA h g^?1 at a current density of 100 mA g^?1, good rate capability and stable cycling performance. When used as electrode materials for supercapacitors, NiCo₂O₄ nanosheets demonstrated a specific capacitance of 400 F g^?1 at a current density of 20 A g^?1 and superior cycling stability over 5000 cycles. The excellent electrochemical performance could be ascribed to the thin porous structure of the nanosheets, which provides a high specific surface area to increase the electrode–electrolyte contact area and facilitate rapid ion transport.     

Ultralight,High Capacitance,Mechanically Strong Graphene-Cellulose Aerogels

With increasing energy demand driving the need for eco-friendly and efficient energy storage technology, supercapacitors are becoming increasingly prevalent in wearable devices because of their portability and stability. The performance of these supercapacitors is highly dependent on the choice of electrode material. The high capacitance and mechanical properties needed for these materials can be achieved by combining graphene’s stable electrical properties with renewable cellulose’s excellent mechanical properties into porous aerogels. In this study, graphene-cellulose hydrogels were prepared by a one-step hydrothermal method, with porous, ultra-light, and mechanically strong graphene-cellulose aerogels then prepared by freeze-drying. These composite aerogels possess excellent mechanical strength and high specific capacitance, capable of bearing about 1095 times the pressure of their own weight. Electrochemical tests show the specific capacitance of these composite aerogels can reach 202 F/g at a scanning rate of 5 mA/cm². In view of their high surface area and fast charge transport provided by their 3D porous structure, graphene-cellulose aerogels have great potential as sustainable supercapacitor electrodes.     

Sn掺杂二氧化锰超级电容器电极材料

用化学液相法制备了超级电容器用的Sn掺杂二氧化锰电极材料. 采用扫描电镜(SEM)、能谱仪(EDS)和X射线衍射(XRD)光谱对电极材料的形貌和物相进行表征. 结果表明, 所得样品由直径约10 nm, 长约100 nm的棒状物粘结成200-500 nm的球状物, 晶型为δ-MnO2. 循环伏安、电化学交流阻抗和恒流充放电测试表明, 化学掺杂的比例对材料的电化学性能有较大的影响. 当Mn:Sn的摩尔比为50:1时, 电极材料的比电容达到293 F·g-1, 比未掺杂的提高了64.6%. 600次充放电循环后, 比电容稳定在275 F·g-1, 表现出良好的容量保持能力.     

Supercapacitor electrodes with especially high rate capability and cyclability based on a novel Pt nanosphere and cysteine-generated graphene

In the present work, supercapacitors based on graphene/Pt films show especially high rate capability (120 F g(-1) even at 50 A g(-1)) and cyclability (no attenuation over 10,000 cycles) and peculiar nanosphere morphology after electrochemical cycling. Furthermore, supercapacitors based on the graphene powder with a binder exhibit high specific capacitance (249 F g(-1) at 0.1 A g(-1)), long cycle life (no attenuation over 40,000 cycles) and high rate capability (150 F g(-1) even at 50 A g(-1)), which are much better than those of most graphene electrode materials. These indicate the great potential of the cysteine reduced graphene electrodes in energy storage.